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Article de journal

Hypersphere Fitting from Noisy Data Using an EM Algorithm

Auteurs : Lesouple Julien, Pilastre Barbara, Altmann Yoann et Tourneret Jean-Yves

IEEE Signal Processing Letters, vol. 28, pp. 314-318, January, 2021.

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This letter studies a new expectation maximization (EM) algorithm to solve the problem of circle, sphere and more generally hypersphere fitting. This algorithm relies on the introduction of random latent vectors having a priori independent von Mises-Fisher distributions defined on the hypersphere. This statistical model leads to a complete data likelihood whose expected value, conditioned on the observed data, has a Von Mises-Fisher distribution. As a result, the inference problem can be solved with a simple EM algorithm. The performance of the resulting hypersphere fitting algorithm is evaluated for circle and sphere fitting.

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Traitement du signal et des images / Observation de la Terre

GNSS Data Demodulation over Fading Environments: Antipodal and M-ary CSK Modulations

Auteurs : Ortega Espluga Lorenzo, Vilà-Valls Jordi, Poulliat Charly et Closas Pau

IET Radar, Sonar & Navigation, January, 2021.

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This article investigates new strategies to compute accurate low-complexity Log Likelihood Ratio (LLR) values based on the Bayesian formulation under uncorrelated fading channels for both antipodal and CSK modulations when no Channel State Information (CSI) is available at the receiver. These LLR values are then used as input to modern error correcting schemes used in the data decoding process of last generation GNSS signals. Theoretical analysis based on the maximum achievable rate is presented for the different methods in order to evaluate the performance degradation with respect to the optimal CSI channel. Finally, Frame Error Rate (FER) simulation results are shown, validating the appropriate performance of the proposed LLR approximation methods.

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Communications numériques / Localisation et navigation et Systèmes spatiaux de communication

Présentation de soutenance de thèse

Onboard IP router for critical aeronautical communications in a heterogeneous environment

Auteur : Tran N'Guyen Hoang Alexandre

Defended on January 20, 2021.

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Critical aeronautical communications are a major issue for flight safety. For a long time, these have relied solely on voice, which is transmitted via an analog communication system. Given the growth in air traffic, this mean of communication has reached saturation and moreover, it has sometimes shown its limits in terms of understanding voice messages, hence the need to find an alternative method. The development of communication technologies based on digital signals allows text messages to be exchanged over a long distance. Initially reserved for noncritical airline operations, it was quickly adopted for communications between the pilot and the air traffic controller, in order to offload the dedicated radio channel. This is known as Data Link. This system, included in a more global infrastructure called the ATN/OSI, has the double advantage of relieving congestion on the frequencies used, but also of limiting the misunderstanding of certain messages. The next evolutions of this aeronautical communication system based on the IP suite and called ATN/IPS is under development. It will have to solve certain problems by proposing new communication technologies and innovative network solutions that can adapt to the increase in critical air data traffic. In this thesis, we address several issues related to the development of ATN/IPS. The first one concerns the network mobility of the aircraft. Indeed, the ATN/IPS will gather several operators, each providing their own subnetworks composed of one or more access methods. Given the limited range of some of them, an aircraft necessarily needs to use several of them during a flight. A handover is triggered as soon as an aircraft connects to a new ground station, which in some cases requires a change in routing to the aircraft. We propose to combine and adapt two mobility protocols, PMIPv6 and LISP, to guarantee continuity of critical data transmission while minimizing the impact on the avionics architecture and the radio communication channel. Our solution is compared to a standard IP mobility solution in a simulated network environment and specifically developed under OMNeT++. The results show that our approach reduces the handover delay, while lightening the signaling traffic on the radio channel. Moreover, in order to propose the best aircraft connectivity, we propose an automation of the selection of the best links in the multilink and ATN/IPS context. Typically, multilink algorithms (or link selection) are split into three parts : collecting link information, deciding which links to use, and using the new links. As the mobility solution proposed in this thesis is also compatible with multilink, we are interested in the first two steps. We propose to use an active method to probe the links and estimate their quality. This approach has the advantage of being independent of the underlying communication technologies. We then compare three estimation methods based on round trip delay and evaluate the performance of each of them. The first method is based on threshold determination, the second is based on a probabilistic model and the third uses supervised learning. This learning-based method makes it possible to estimate the link over time with good precision. Finally, we propose a link selection algorithm in the case where the primary link no longer meets the quality of service requirements.

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Réseaux / Systèmes de communication aéronautiques

Brevet

Codage LDPC à Protection Différenciée

Auteurs : Ortega Espluga Lorenzo, Poulliat Charly, Al Bitar Hanaa, Boucheret Marie-Laure et Aubault-Roudier Marion

n° FR3097388, BOPI 2020-51, December 18, 2020.

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The invention provides a new method of unequal error protection which is based on a particular parity matrix structure for LDPC-type codes - Figure 1.

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Communications numériques / Systèmes spatiaux de communication

Article de conférence

Robust Tracking under Measurement Model Mismatch via Linearly Constrained Extended Kalman Filtering

Auteurs : Ortega Espluga Lorenzo, Vilà-Valls Jordi, Chaumette Eric, Pages Gaël et Vincent François

In Proc. 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, December 14-18, 2020.

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Standard state estimation techniques, ranging from the linear Kalman filter to nonlinear sigma-point or particle filters, assume a perfectly known system model, that is, process and measurement functions and system noise statistics (both the distribution and its parameters). This is a strong assumption which may not hold in practice, reason why several approaches have been proposed for robust filtering. In the context of linear filtering, a solution to cope with a possible system matrices mismatch is to use linear constraints. In this contribution we further explore the extension and use of recent results on linearly constrained Kalman filtering (LCKF) for robust tracking/localization under measurement model mismatch. We first derive the natural extension of the LCKF to nonlinear systems, and its use to mitigate parametric modelling errors in the nonlinear measurement function. A tracking problem where a set of sensors at possibly mismatched (unknown to a certain extent) positions track a moving object from time of arrival measurements is used to support the discussion.

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Traitement du signal et des images / Localisation et navigation et Systèmes spatiaux de communication

A Compact CRB for the Single Source Conditional Signal Model with Application to Delay-Doppler-Phase Estimation of Band-Limited Signals

Auteurs : Ortega Espluga Lorenzo, Medina Daniel, Vilà-Valls Jordi, Vincent François et Chaumette Eric

In Proc. 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, December 14-18, 2020.

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The derivation of tight estimation lower bounds is a key player to design and assess the performance of new estimators. In this contribution, we derive a new compact Cramér-Rao bound (CRB) for the conditional signal model, where the deterministic parameter's vector includes a real positive amplitude and the signal phase. Then, such CRB is particularized to the delay, Doppler, phase and amplitude estimation with band-limited (narrowband) signals, where transmitter and receiver are in relative uniform radial movement. The latter expression is especially easy to use because it only depends on the signal samples. We provide illustrative results for a representative Global Navigation Satellite System positioning example.

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Traitement du signal et des images / Localisation et navigation et Systèmes spatiaux de communication

Reactivity Enhancement of Cooperative Congestion Control for Satellite Networks

Auteurs : Thibaud Adrien, Fasson Julien, Arnal Fabrice, Sallantin Renaud, Dubois Emmanuel et Chaput Emmanuel

In Proc. Hot Information-Centric Networking (HotICN), Hefei, Anhui, China, December 12-14, 2020.

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The new paradigm of Information Centric Network (ICN) proposes a shift from the host-centric model to a contentcentric model. This approach, especially well suited to the current Internet’s usage, is promising for Satellite Networks. In particular, Named Data Networking (NDN) architecture seems to be a great candidate: it gathers the benefits of Content Delivery Networks (CDN), Peer-to-Peer networks (P2P) and HTTP in the network layer. In this study, we propose to compare the performances of TCP-like congestion control algorithms and our new Cooperative Congestion Control (CCC) approach. CCC is a pace-based multipath and multi-flow aware congestion control. We evaluate those algorithms with simulations on a topology where we place the satellite link on different positions. We show that CCC outperforms window-based algorithms but has still some drawbacks. We thus proposed an enhancement of CCC that corrects the flaws by increasing its reactivity. Simulations results show that the performances on terrestrial scenarios are also enhanced.

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Réseaux / Autre

Article de journal

Joint Delay-Doppler Estimation Performance in a Dual Source Context

Auteurs : Lubeigt Corentin, Ortega Espluga Lorenzo, Vilà-Valls Jordi, Lestarquit Laurent et Chaumette Eric

Remote sensing, vol. 12, issue 3, p. 3894, November, 2020.

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Evaluating the time-delay, Doppler effect and carrier phase of a received signal is a challenging estimation problem that was addressed in a large variety of remote sensing applications. This problem becomes more difficult and less understood when the signal is reflected off one or multiple surfaces and interferes with itself at the receiver stage. This phenomenon might deteriorate the overall system performance, as for the multipath effect in Global Navigation Satellite Systems (GNSS), and mitigation strategies must be accounted for. In other applications such as GNSS reflectometry (GNSS-R) it may be interesting to estimate the parameters of the reflected signal to deduce the geometry and the surface characteristics. In either case, a better understanding of this estimation problem is directly brought by the corresponding lower performance bounds. In the high signal-to-noise ratio regime of the Gaussian conditional signal model, the Cramér-Rao bound (CRB) provides an accurate lower bound in the mean square error sense. In this article, we derive a new compact CRB expression for the joint time-delay and Doppler estimation in a dual source context, considering a band-limited signal and its specular reflection. These compact CRBs are expressed in terms of the baseband signal samples, making them especially easy to use whatever the baseband signal considered, therefore being valid for a variety of remote sensors. This extends existing results in the single source context and opens the door to a plethora of usages to be discussed in the article. The proposed CRB expressions are validated in two representative navigation and radar examples.

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Traitement du signal et des images / Localisation et navigation

Seeing around corners with edge-resolved transient imaging

Auteurs : Rapp Joshua, Saunders Charles, Tachella Julian, Murray-Bruce John, Altmann Yoann, Tourneret Jean-Yves, McLaughlin Stephen, Dawson Robin M. A., Wong Franco N.C. et Goyal Vivek K.

Nat. Commun., vol. 11, no. 1, pp. 5929, November 23, 2020.

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Non-line-of-sight (NLOS) imaging is a rapidly growing field seeking to form images of objects outside the field of view, with potential applications in autonomous navigation, reconnaissance, and even medical imaging. The critical challenge of NLOS imaging is that diffuse reflections scatter light in all directions, resulting in weak signals and a loss of directional information. To address this problem, we propose a method for seeing around corners that derives angular resolution from vertical edges and longitudinal resolution from the temporal response to a pulsed light source. We introduce an acquisition strategy, scene response model, and reconstruction algorithm that enable the formation of 2.5-dimensional representations—a plan view plus heights—and a 180∘ field of view for large-scale scenes. Our experiments demonstrate accurate reconstructions of hidden rooms up to 3 meters in each dimension despite a small scan aperture (1.5-centimeter radius) and only 45 measurement locations.

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Traitement du signal et des images / Autre

Thèse de Doctorat

Estimation Parcimonieuse et Apprentissage de Dictionnaires pour la Détection d'Anomalies Multivariées dans des Données Mixtes de Télémesure Satellite

Auteur : Pilastre Barbara

Defended on November 6, 2020.

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La surveillance automatique de systèmes et la prévention des pannes sont des enjeux majeurs dans de nombreux secteurs et l’industrie spatiale ne fait pas exception. Par exemple, le succès des missions des satellites suppose un suivi constant de leur état de santé réalisé à travers la surveillance de la télémesure. Les signaux de télémesure sont des données issues de capteurs embarqués qui sont reçues sous forme de séries temporelles décrivant l’évolution dans le temps de différents paramètres. Chaque paramètre est associé à une grandeur physique telle qu’une température, une tension ou une pression, ou à un équipement dont il reporte le fonctionnement à chaque instant. Alors que les approches classiques de surveillance atteignent leurs limites, les méthodes d’apprentissage automatique (machine learning en anglais) s’imposent afin d’améliorer la surveillance de la télémesure via un apprentissage semi-supervisé : les signaux de télémesure associés à un fonctionnement normal du système sont appris pour construire un modèle de référence auquel sont comparés les signaux de télémesure récemment acquis. Les méthodes récentes proposées dans la littérature ont permis d’améliorer de manière significative le suivi de l’état de santé des satellites mais elles s’intéressent presque exclusivement à la détection d’anomalies univariées pour des paramètres physiques traités indépendamment. L’objectif de cette thèse est de proposer des algorithmes pour la détection d’anomalies multivariées capables de traiter conjointement plusieurs paramètres de télémesure associés à des données de différentes natures (continues/discrètes), et de prendre en compte les corrélations et les relations qui peuvent exister entre eux. L’idée motrice de cette thèse est de supposer que la télémesure fraîchement reçue peut être estimée à partir de peu de données décrivant un fonctionnement normal du satellite. Cette hypothèse justifie l’utilisation de méthodes d’estimation parcimonieuse et d’apprentissage de dictionnaires qui seront étudiées tout au long de cette thèse. Une deuxième forme de parcimonie propre aux anomalies satellites a également motivé ce choix, à savoir la rareté des anomalies satellites qui affectent peu de paramètres en même temps. Dans un premier temps, un algorithme de détection d’anomalies multivariées basé sur un modèle d’estimation parcimonieuse est proposé. Une extension pondérée du modèle permettant d’intégrer de l’information externe est également présentée ainsi qu’une méthode d’estimation d’hyperparamètres qui a été développée pour faciliter la mise en œuvre de l’algorithme. Dans un deuxième temps, un modèle d’estimation parcimonieuse avec un dictionnaire convolutif est proposé. L’objectif de cette deuxième méthode est de contourner le problème de non-invariance par translation dont souffre le premier algorithme. Les différentes méthodes proposées sont évaluées sur plusieurs cas d’usage industriels associés à de réelles données satellites et sont comparées aux approches de l’état de l’art.

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Traitement du signal et des images / Autre

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